All drug discrimination procedures currently utilized provide for multiple training trials within a session. This allows the stimulus properties of the reinforcer (i.e., presence or absence of reinforcement following choice behavior on trial one) to mediate choice behavior on all subsequent trials within the session. The acquisition of discriminative control of choice behavior by the drug cue may be hindered by the presence of the reinforcer cue. The proposed experiments investigate the effects of the reinforcer cue in drug discrimination procedures upon the control exerted by the drug cue. A novel drug discrimination procedure which provides for only one choice trial per session (and, therefore, abolishes the cue value of the reinforcer as a mediator of choice behavior) is compared with a representative procedure which provides for multiple choice trials per session. The one-trial procedure may enhance the effectiveness of the drug cue, and, consequently, provide a drug discrimination methodology which is more sensitive to the object of such research (i.e., the stimulus properties of drugs).